1. Field of the Invention
The present invention relates to a power supply voltage monitoring circuit capable of reducing a minimum operating power supply voltage in an electronic circuit so as to allow the electronic circuit to operate at a reduced power supply voltage, and an electronic circuit including the power supply voltage monitoring circuit.
2. Description of the Related Art
For an electronic circuit, an operation-enabled power supply voltage range best suited to the circuit is defined. In the operation-enabled power supply voltage range, proper operation of the circuit is ensured, and therefore the reliability of a signal to be output from the circuit is secured.
When the electronic circuit is turned on, the power supply voltage transiently increases to the operation-enabled power supply voltage, and hence a state transition is effected in which the power supply voltage increases to the operation-enabled power supply voltage. In order to ensure the reliability of a signal to be output during the state transition, the electronic circuit employs a method of controlling and fixing a signal to be output (see, for example, JP 08-279739 A; hereinafter, referred to as Patent Document 1).
An example of the method includes a method of providing a power supply voltage monitoring circuit so as to monitor a power supply voltage to be input, to thereby detect a low power supply voltage state. For example, in the power supply voltage monitoring circuit illustrated in FIG. 1 of Patent Document 1, a power supply voltage to be supplied to the electronic circuit 20 is monitored, and when the power supply voltage becomes equal to or larger than a predetermined set value, an operation-enabled signal is supplied to the electronic circuit 20. With this configuration, the electronic circuit 20 may be prevented from causing malfunction.
The power supply voltage monitoring circuit disclosed in Patent Document 1 includes the power supply voltage detecting circuit as described above, which employs a breeder resistor to detect a power supply voltage. In other words, the power supply voltage monitoring circuit employs an additional circuit for detecting that the power supply voltage becomes equal to or larger than the minimum operating power supply voltage, the additional circuit being different from the circuit to be originally ensured the minimum operating power supply voltage. This configuration is inefficient in a sense that the power supply voltage may not be efficiently used in the electronic circuit.
In other words, the electronic circuit may desirably be configured such that, when a power supply voltage has exceeded the minimum operating power supply voltage in the circuit which needs to be originally ensured the minimum operating power supply voltage, the circuit immediately transmits the information thereon to an external circuit. With this configuration, the minimum operating power supply voltage may be reduced, to thereby reduce the minimum operating power supply voltage requirements in an electronic circuit, such as an integrated circuit (IC).